50 Dr. W. C. Williamson on 



6 mm., that of the medulla 4*2, and the number of the 

 primary tracheids 1292. In C.N. 1649, the branch has 

 increased in size. The primary cylinder has a diameter of 

 7'2 mm., its tracheids are 2350, and its medulla is enlarged 

 to 5*2 mm. In C.N. 1592, the diameter of the primary 

 cylinder is again j - 2 mm. ; its tracheids are 2^24 ; and its 

 medulla 57. We have another somewhat parallel example 

 in C.N. 1648, where the entire section has a mean diameter 

 of 60 mm., that of the Primary Xylem cylinder being 7 mm. 

 Its tracheids are 1847 in number and its medulla has a 

 mean diameter of 5 mm. The number of the tracheids 

 composing that cylinder increased successively to 1292, to 

 1847, to 2241, and to 2350, and following these pro- 

 gressive advances in the tracheal mass, there was a corres- 

 ponding enlargement of the central medulla beginning at 

 2 mm. to 2-5 — 4-2, 5 — 5-2 — 5-2 and 57. 



Dichotomies — Equal. 



Of this condition I have only obtained one example of 

 the fuliginosiwi type, but this is the largest specimen of the 

 type that my cabinet contains. The section has the usual 

 oval form, its longer diameter being 130 mm., and its 

 shorter one 60 mm. Its two primary cylinders have 

 dimensions corresponding to those of the branch as a whole. 

 One of them is crushed, but the other is perfect. The mean 

 diameter of the latter one above is 87 mm. and contains 2195 

 tracheids. The two cylinders combined must have consisted 

 of more than four thousand tracheids, and the one medulla 

 of this one cylinder alone has enlarged to 6 mm. 



Dichotomies — Unequal. 



Of these we have several very interesting examples. 

 In 379 — © we have detached a strongly marked and com- 

 plete semicircular segment and carrying along with it a 

 peripheral investment of the innermost cortex of the parent 



